-LRB- CNN -RRB- -- Suspected cop killer Eric Matthew Frein appears to have left handwritten notes in the Pennsylvania woods in which he chillingly describes his ambush of two state troopers last month , State Police Lt. Col. George Bivens said Wednesday .

`` Friday September 12 , got a shot around 11 p.m. and took it . He dropped ... I took a follow up shot on his head , neck area . He was still and quiet after that . Another cop approached the one I just shot . As he went to kneel , I took a shot at him and he jumped in the door . His legs were visible and still , '' the note reads , according to Bivens .

CNN first reported on the handwritten notes on Monday .

Frein , 31 , is suspected in the September 12 ambush that left Cpl. Bryon Dickson dead and Trooper Alex T. Douglass wounded outside the Pennsylvania State Police barracks in Blooming Grove .

Bivens said Frein faces two additional counts of possession of a weapon of mass destruction after two booby trapped pipe bombs were discovered in the Pocono Mountains search area last week .

Authorities said a search of Frein 's bedroom turned up a variety of black and synthetic powders -- material consistent with what was used to make the two pipe bombs . In the search of his bedroom , investigators also found galvanized steel pipes drilled out to accept fusing material , end caps , pyrotechnic fuse and improvised explosive initiators .

`` The design is simple but very dangerous and could have caused significant injury to anyone in the vicinity of that explosive , '' said Sam Rabadi , special agent in charge of ATF in Pennsylvania .

Who is Eric Frein ?

Bivens said the handwritten notes were discovered among items left behind at a campsite located by law enforcement agents on September 29 .

After the shooting , Frein supposedly wrote , `` I ran back to the jeep . I made maybe half a mile ... and hit a road block . I did n't expect one so soon . It was only 15 to 20 minutes . ''

Bivens quoted the suspect as writing that he `` did a k turn a quarter mile from them and pulled into a development I knew had unfinished access road . Hearing helos , I just used my marker lights , missed the trail around a runoff pool and drove straight into it . Disaster . Made half attempt to stash AK and ran . ''

A massive search for Frein has been carried out since , at times involving as many as 1,000 officers . Despite recent sightings and other leads , he has eluded authorities . The manhunt has cost several million dollars , Bivens said .

Authorities have said that a review of a computer hard drive used by Frein shows that he had planned the attack for years .

Frein has been described as a survivalist and military reenactment enthusiast with a hatred for law enforcement , authorities say .

CNN 's David Shortell and Steve Kastenbaum contributed to this report .

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Eric Frein appears to have left notes after allegedly killing cop in Pennsylvania

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Frein , 31 , suspected in September 12 ambush of 2 officers ; 1 died

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Police say he planned attack for years